The aim of this project was to investigate the cyclisation reactions of some o-nitroaryl derivatives of amino acids, with a view to the synthesis of potentially biologically active heterocyclic compounds. Chapter one is concerned with an overview of the synthesis of heterocyclic N-oxides, mainly via the cyclisations of ortho-substituted nitroaromatics. Firstly, the properties of heterocyclic N-oxides are considered, then both reductive and non-reductive methods of their synthesis by cyclisation reactions are explored. After a discussion of intramolecular condensations leading to cyclisation, the possibilities for alternative mechanisms for these reactions are deliberated. Chapter Two begins with an introduction to the specific cyclisation reactions of o-nitroaryl- and 2, 4-dinitrophenyl-amino acids. The preparation and cyclisation reactions of o-nitrophenyl derivatives of amino acid esters are then described with emphasis on the implications for the mechanism of these cyclisation reactions. Chapter Three discusses the related cyclisations of N-alkyl-o-nitroanilines which have no activating group (for example, an ester) on the N-alkyl chain. The mechanistic implications of this are explored, in the context of the cyclisations discussed in Chapter Two. In Chapter Four, the synthesis of benzimidazole and quinoxaline acyclic nucleoside analogues is briefly described. These have the potential to be biologically active compounds.